{"id":"CVE-2026-69207","aliases":["GHSA-8j4g-w8fx-2239"],"url":"https://o3.security/vulnerability/CVE-2026-69207","summary":"Hono: ReDoS in CORS middleware via Access-Control-Request-Headers","details":"### Summary\n\nThe built-in CORS middleware (`hono/cors`) parses the attacker-controlled `Access-Control-Request-Headers` request header during a preflight (`OPTIONS`) request using a regular expression whose running time is quadratic in the input length. A single request carrying a long run of whitespace can consume seconds of CPU, and repeated requests can render the service unresponsive. This parsing runs under the default configuration.\n\n### Details\n\nOn a CORS preflight, when `allowHeaders` is not configured - the default - the middleware reflects and parses the `Access-Control-Request-Headers` value. The parser used a whitespace-tolerant regular expression whose backtracking makes the work grow quadratically (O(n²)) with the length of the value when it contains a long whitespace sequence without a delimiter.\n\nBecause the header value is bounded only by the deployment's maximum HTTP header size, a single preflight can block request processing for a noticeable amount of time; on runtimes that share one execution thread across requests, this stalls concurrent requests as well. No authentication, special origin, or user interaction is required.\n\nThis issue arises for any application using `cors()` with the default (or an empty) `allowHeaders`. Applications that set a non-empty `allowHeaders` do not reach the affected path.\n\n### Impact\n\nAn unauthenticated attacker can send preflight requests that each consume disproportionate CPU relative to their size, degrading or denying service. This is a denial-of-service issue only; it does not expose or modify data.","published":"2026-08-07T20:51:04.300Z","modified":"2026-10-28T02:30:51.296601611Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.00488,"percentile":0.40916,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"hono","fixedVersion":"4.12.34"}],"fix":{"url":"https://github.com/honojs/hono/commit/93fc250d8b4df58ea542cb945171de8013d5e6d5","label":"honojs/hono@93fc250"},"references":[{"type":"WEB","url":"https://github.com/honojs/hono/releases/tag/v4.12.34"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/69xxx/CVE-2026-69207.json"},{"type":"ADVISORY","url":"https://github.com/honojs/hono/security/advisories/GHSA-8j4g-w8fx-2239"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-69207"},{"type":"FIX","url":"https://github.com/honojs/hono/commit/93fc250d8b4df58ea542cb945171de8013d5e6d5"},{"type":"PACKAGE","url":"https://github.com/honojs/hono"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:51.296601611Z"}}